The invention relates to mirror reflex cameras of the single lens type, where the finder image is formed by light coming through the same lens through which light reaches the sensitized film when an exposure is made. Such cameras are well known in the art. In most such cameras, the reflex mirror is pivoted to tilt or swing from viewing position to picture-taking position and vice versa. This is the common practice in single lens mirror reflex cameras designed to take film of the conventional 35 millimeter width. It is difficult, however, to find adequate room for the swinging mirror and other parts necessarily associated therewith, if it is desired to produce a truly miniature camera, taking film with considerably less width than 35 millimeters.